<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>

<body>
    <ul>
        <li>Jack</li>
        <li>Rose</li>
        <li>Mark</li>
    </ul>

    <script>
        var users = document.getElementsByTagName("li");
        for (let i = 0; i < users.length; i++) { //修改为let
            users[i].addEventListener("click", function () {
                alert(this.innerText + "," + i);
            }, false);
        }
        console.log(i);
    </script>

</body>

</html>